1. Field of the Invention
The present invention relates generally to a slide type exhaust brake system which is connected midway of the exhaust pipe of a large-sized vehicle such as a motor truck or an omnibus to exert a braking function to the vehicle by closing the exhaust flow passage of engine exhaust gases when the vehicle is running steep downhill and, more particularly, to an improvement in the structure of a pressure regulating valve of the slide type exhaust brake system.
2. Description of the Prior Art
As the exhaust brake system of this type, there is known U.S. Pat. No. 4,205,704. The pressure regulating valve disclosed in this U.S. Patent will be described in detail with reference to FIG. 5. A primary gate 13 having a waste gate port 14 in its surface is fitted in a reciprocation passage formed in a body housing of the exhaust brake system. A pressure regulating valve 17 is disposed in the vicinity of the leading end of a piston rod 16 of an air cylinder mechanism. A waste gate seal 19 slides on the surface of a waste gate 18 at the side of the primary gate 13. The waste gate seal 19 and the waste gate 18 are loosely fitted on each other to have their slot 18' and bulging wall 19' engaging with each other.
However, the pressure regulating valve 17 of the prior art is compelled in its design to be fitted loosely at its restricted portion by the limited size of the primary gate 13 and by the least size of the waste gate 18 required for the smooth operation of the primary gate 13. Moreover, the loosely engaging portions are caused to "chatter" by the loose engagement and by the impact of the waste gate 18 upon the primary gate 13 when the passage is to be closed due to the frequent reciprocations of the primary gate 13. The chattering in turn causes the waste gate seal 19 to incline in the longitudinal direction to establish an arcuate wear on the sliding face when in the reciprocations for opening or closing the passage. This raises a problem that the close fit of the waste gate port 14 in the closed state is deteriorated to invite leakage of the exhaust gases thereby to drop the braking function. In order to eliminate this problem, on the other hand, the waste gate 18 and the seal 19 including their slot 18' and bulging wall 19' have to be precisely cast to remarkably block the productivity.